1. Field of the Invention
This invention relates to power distribution systems, particularly those using inductive power transfer from high frequency resonant currents within the primary conductors, and more particularly to modular resonant magnetic field emitter units.
2. Description of the Related Art
Long-standing problems exist in the conventional transfer of electric power to self-powered moving vehicles. Those having a sliding brush rubbing along a fixed current-carrying conductive rail exhibit wear, dust production, intermittent loss of electrical contact, sparking, and electric shock hazards. Vehicles lacking the guidance of weight-bearing rails are particularly prone to wander away from a defined route and are then likely to lose electrical contact with a supply conductor.
Inductive power distribution systems overcome many of the problems by using the alternating magnetic field surrounding a fixed primary conductor to induce current in a secondary conductor at some distance from the primary conductor, thereby avoiding direct contact. They are particularly suited to providing motive power.
The use of high-frequency resonating currents within primary and secondary conductors has greatly improved the efficiency of inductive power distribution, and recent developments in semiconductor technology have permitted the application of improved inductive power systems as have been described by Boys & Green in WO 92/17929.
Resonant inductive power transfer systems been hampered by the difficulty of driving long tracks with sufficient power. Although a track of a given length can be supplied with more power simply by using higher voltages, reasonable safety requirements may be exceeded, and the ratings of presently available electronic components used in the power supply will generally be exceeded with output voltages above 600 V.
A further drawback of such systems is the risks to health understood to be caused by strong magnetic fields radiated by current-carrying conductors; risks that have resulted in stringent field strength guidelines being adopted. Delivery of realistic amounts of energy for motive power purposes is usually likely to breach these restrictions.